Ingan-based light-emitting diode chip and a method for the production thereof

ABSTRACT

A light-emitting diode chip ( 1 ), in which over a substrate ( 2 ), a series of epitaxial layers ( 3 ) with a radiation-emitting active structure ( 4 ) based on InGaN is disposed. Between the substrate ( 2 ) and the active structure ( 4 ), a buffer layer ( 20 ) is provided. The material or materials of the buffer layer ( 20 ) are selected such that their epitaxial surface ( 6 ) for the epitaxy of the active structure ( 4 ) is unstressed or slightly stressed at their epitaxial temperature. The active structure ( 4 ) has In-rich zones ( 5 ), disposed laterally side by side relative to the epitaxial plane, in which zones the In content is higher than in other regions of the active structure ( 4 ). A preferred method for producing the chip is disclosed.

This application is a U.S. National Phase Application under 35 USC 371of International Application PCT/DE01/02190 (not published in English)filed 13 Jun. 2001.

FIELD OF THE INVENTION

The invention relates to an InGaN-based light-emitting diode chip and toa method for producing an InGaN-based light-emitting diode chip.

BACKGROUND OF THE INVENTION

The term InGaN-based light-emitting diode chips in conjunction with thepresent invention is understood fundamentally to mean all light-emittingdiode chips whose radiation-emitting zone has InGaN or related nitridesas well as mixed crystals based thereon, such as Ga(Al,In)N.

InGaN-based light-emitting diode chips are known for instance from TheBlue Laser Diode by Shuji Nakamura and Gerhard Fasol, Springer VerlagBerlin Heidelberg 1997, page 209 ff.

SUMMARY OF THE INVENTION

An object of the invention is to make a light-emitting diode chip of thetype defined at the outset available that has the highest possibleradiation intensity.

This and other objects are attained in accordance with one aspect of thepresent invention directed to a light-emitting diode chip, having aseries of epitaxial layers with a radiation-emitting active structurebased on InGaN is grown on a substrate. Between the substrate and theradiation-emitting active structure is a buffer layer, comprising one ormore layers. The material or materials of the buffer layer are selectedsuch that their epitaxial surface for the epitaxy of theradiation-emitting active structure is unstressed or slightly stressedat their epitaxial temperatures. The radiation-emitting active structurehas zones richer in In disposed laterally side by side relative to theepitaxial plane, in which zones the In content is higher than in otherregions of the active structure.

In a preferred refinement of the light-emitting diode chip, thesubstrate substantially comprises electrically conductive SiC. As aresult, the chip can advantageously be realized with a typicallight-emitting diode chip structure, in which the contact faces aredisposed on opposed sides of the chip. Consequently, current impressionover a large region of the lateral chip cross section is possible in asimple way. In contrast to this, in chips with an electricallyinsulating substrate, the side toward the substrate of the series ofepitaxial layers must be contacted from their surface. This involvesmarkedly greater production complexity and expense, because the seriesof epitaxial layers, after being produced, have to be provided withetched trenches or grown in structured fashion in order to be able tocontact the n-side of the active structure.

In an especially preferred refinement of the light-emitting diode chip,the active structure has a multiple-quantum-well structure, in which atleast one quantum well contains the In-rich zones.

Especially preferably, the series of buffer layers has an AlGaN:Si thatis a few hundred nanometers thick and is followed in the growthdirection by a GaN:Si layer. The latter has a thickness between 1 μm and3 μm. The surface of the GaN:Si layer forms the epitaxial surface forthe epitaxy of the radiation-emitting epitaxial layer series and at theepitaxial temperature or epitaxial temperatures of the InGaN-basedlayer, it is unstressed or slightly stressed.

Another aspect of the present invention is directed to a method in whicha radiation-emitting epitaxial layer series with a radiation-emittingactive structure based on InGaN is deposited over a substrate. Beforethe epitaxy of the radiation-emitting active structure, a buffer layeror a series of buffer layers is grown on the substrate, the epitaxialsurface of which layer or series, for the growth of theradiation-emitting active structure, is unstressed or slightly stressedat the epitaxial temperature or temperatures thereof.

With this method, it is advantageously achieved that the activestructure has In-richer zones disposed laterally side by side relativeto the epitaxial plane, in which zones the In content is higher than inother regions of the active structure.

In an especially preferred embodiment of the method, as the activestructure,

As the buffer layer, preferably over the substrate first an AlGaN:Silayer a few hundred nanometers thick is deposited epitaxially, overwhich a GaN:Si layer is grown epitaxially. The thickness of the GaNSi:layer is between 1 μm and 3 μm, and over its surface, theradiation-emitting epitaxial layer series is deposited.

As the epitaxy method, metal-organic vapor phase epitaxy (MOVPE) ispreferably suitable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a, a schematic illustration of a section through a firstexemplary embodiment;

FIG. 1 b, a schematic illustration of an advantageous contact design andof an advantageous way of mounting the first exemplary embodiment;

FIG. 2, a schematic illustration of a section through a second exemplaryembodiment, including its advantageous type of mounting.

DETAILED DESCRIPTION OF THE DRAWINGS

In the drawings of the various exemplary embodiments, components thatare the same or function the same are each identified by the samereference numerals.

In the light-emitting diode chip 1 of FIG. 1 a, a radiation-emittingactive structure 4 is disposed over an SiC substrate 2. In the presentexample, this active structure has an InGaN single quantum well 7.

The radiation-emitting active structure 4 includes a plurality ofIn-rich zones 5, disposed laterally side by side relative to theepitaxial plane, in which zones the In content is higher than in theother regions of the active structure 4. The In content in the In-richzones 5 is for instance up to 40%.

Over the radiation-emitting active structure 4, a thin p-conductivelydoped AlGaN epitaxial layer 8 and a p-conductively doped GaN layer 9that is for instance 200 nm thick are grown.

It is equally possible for instance to provide an InGaN-basedradiation-emitting active structure 4 with a double-hetero structure ora multiple-quantum-well structure (MQW) structure with a plurality ofquantum wells.

The SiC substrate 2 is electrically conductive and is at least partlypermeable to the radiation emitted by the epitaxial layer series 3.

Between the substrate 2 and the active structure 4 is a buffer layer 20,which contains an AlGaN:Si layer 10 a few hundred nanometers thick,which is followed in the growth direction by a GaN:Si layer 11. TheGaN:Si layer 11 has a thickness between 1 μm and 3 μm, and its surfacefacing away from the substrate 2, in the production of the chip 1, formsthe epitaxial surface 6 for the epitaxy of the InGaN-basedradiation-emitting active structure 4.

In the contact design and type of mounting of the chip of FIG. 1 b,which with respect to its epitaxial layer structure 3 is equivalent tothe chip 1 of FIG. 1 a, a bondable p-contact layer 12 is applied to thep-conductively doped GaN layer 9. This contact layer comprises Ag, or aPtAg and/or PdAg alloy, or is composed for instance of a first layerthat is permeable to radiation and a reflective second layer. In thesecond alternative, the first layer essentially comprises Pt and/or Pd,for instance, and the second layer substantially comprises Ag, Au,and/or Al, or a dielectric mirror layer, for instance.

On its side 15 facing away from the epitaxial layer series 3, the SiCsubstrate 2 is provided with a contact metallization 13, which coversonly part of this primary face 15 and is embodied as a bond pad for wirebonding.

The chip 1 is mounted by means of die bonding with its p-side, that is,the p-contact layer 12, on a chip mounting face 19 of an electricleadframe 14. The n-contact metallization 13 is connected via a bondwire 17 to a connection part 18 of the leadframe 14.

The light output from the chip 1 is effected via the free region of theprimary face 15 of the SiC substrate 2 and via the chip edges 16.

Optionally, the chip 1 has an SiC substrate 2 that is thinned after theepitaxy of the epitaxial layer series 3. It is equally possible for thesubstrate 2, after the epitaxy of the epitaxial layer series 3, to beremoved completely from this layer or series, creating a so-calledthin-film LED.

It is understood that the chip 1 of the invention can also be mountedwith its substrate side, that is, so-called “up side up” mounting, onthe chip mounting face 13 of an electrical leadframe 14. The contactdesign should then naturally be adapted to that type of mounting.Possible materials for suitable contact metallization are known from theprior art and will therefore not be described further at this point.

The exemplary embodiment shown in FIG. 2 differs from that of FIGS. 1 aand 2 b essentially in that the chip edges 16 in the region below theactive structure 4 are oblique to the primary direction in which thequantum well 7 extends; in the further course toward the underside, theythen change over to side faces that are perpendicular again to theprimary direction in which the quantum well 7 extends, so that on theone hand improved output of the radiation generated in the active zonethrough the side faces is attained, and on the other, reliable flip-chipmounting with conventional chip mounting systems is possible. The angleα of the regions of the side faces that are oblique to the quantum wellis preferably between 20° and 80°, and an angle of approximately 30° isespecially advantageous.

This chip structure of FIG. 2 is created by means of a shaping sawblade, whose end face is V-shaped and with which the epitaxy wafer,before the separation into individual chips 1, is sawn into the shapeshown in FIG. 2.

In a method for producing a light-emitting component of the exemplaryembodiments, first by means of metal organic gas phase epitaxy (MOVPE),the AlGaN:Si layer 10 a few hundred nanometers thick and the GaN:Silayer 11 are applied to the substrate 2. Next, the radiation-emittingactive structure 4 is deposited, in which the epitaxial surface intendedfor it, which in the present case is formed by the free primary face ofthe GaN:Si layer 11, is unstressed or slightly stressed at the epitaxialtemperature or temperatures of the InGaN-based structure.

Below, a comparison test of two chips 1 produced identically except forthe epitaxial surface of the GaN:Si layer 11 by the method describedabove will be explained.

Sample 1 is a chip in which the epitaxial surface 6 is severelycompressively stressed at the epitaxial temperature of the InGaN-basedlayer.

Conversely, in sample 2, the epitaxial surface 6 has no tension or onlyslight tension at the epitaxial temperature of the InGaN-based layer.

An analysis of the chips shows that the sample 1 has very smoothboundary faces between the various epitaxial layers of the series ofactive layers and has a homogeneous In content of approximately 15%.Conversely in sample 2, the boundary faces between the various epitaxiallayers of the active layer series are very rough, and the structure hasdotlike locally raised lattice constants, which correspond with locallyincreased In contents of up to 40%.

When mounted in a 5-mm radial structural form with a 20 mA forwardcurrent, sample 2 has a markedly increased performance over sample 1,with a simultaneous shift in the peak wavelength toward greaterwavelengths.

It is understood that the explanation of the invention in terms of theabove exemplary embodiments is not to be understood as a limitation tothese embodiments. On the contrary, the invention can be used inparticular in all light-emitting diode chips in which the active zone isbased on InGaN.

1. A light-emitting diode chip, comprising: a series of epitaxial layersincluding a radiation-emitting, InGaN-based active structure disposedover a substrate, and a buffer layer having at least one layer, thebuffer layer being disposed between the substrate and the activestructure, wherein material forming the buffer layer is such that anepitaxial surface thereof for epitaxy of the active structure isunstressed or slightly stressed at their epitaxial temperature, theepitaxial surface for epitaxy of the active structure being on thebuffer layer, and wherein the active structure has In-rich zonesdisposed laterally side by side in a plane which is parallel to saidepitaxial surface, and wherein an In content in the In-rich zones ishigher than in other regions of the active structure.
 2. Thelight-emitting diode chip of claim 1, wherein the substratesubstantially comprises SiC.
 3. The light-emitting diode chip of claim1, wherein the active structure has a single-quantum-well structure or amultiple-quantum-well structure that contains the In-rich zones.
 4. Thelight-emitting diode chip of claim 1, wherein the buffer layer comprisesa series of buffer layers including an AlGaN:Si layer and a GaN:Si layerlocated downstream thereof in a direction of growth, the GaN:Si layerhaving a thickness of between 1 μm and 3 μm and a surface that forms theepitaxial surface for epitaxy of the active structure.
 5. A method forproducing an InGaN-based light-emitting component by depositing on asubstrate a series of epitaxial layers which include aradiation-emitting InGaN-based active structure and a buffer layer,wherein the method comprises the steps of: selecting material formingthe buffer layer such that an epitaxial surface of the buffer layer forepitaxy of the radiation-emitting active structure is unstressed orslightly stressed at their epitaxial temperatures; epitaxially growingthe buffer layer over the substrate from said selected material; andepitaxially growing the active structure over said epitaxial surface ofthe buffer layer, wherein said active structure has In-rich zonesdisposed laterally side by side in a plane which is parallel to saidepitaxial surface, and wherein an In content in the In-rich zones ishigher than in other regions of the active structure.
 6. The method ofclaim 5, wherein the active structure comprises a multiple-quantum-wellstructure having an InGaN quantum well.
 7. The method of claim 5,wherein the substrate comprises SiC.
 8. The method of claim 5, whereinthe method comprises the steps of: forming the buffer layer by a.forming an AlGaN:Si layer having a thickness of a few hundred nanometersover the substrate, and b. forming a GaN:Si layer having a thickness ofbetween 1 μm and 3 μm over the AlGaN:Si layer; and in said step offorming the radiation-emitting active structure, said active structureis formed on a surface of the GaN:Si layer.
 9. The method of claim 6,wherein the method comprises the steps of: forming the buffer layer bya. forming an AlGaN:Si layer having a thickness of a few hundrednanometers over the substrate, and b. forming a GaN:Si layer having athickness of between 1 μm and 3 μm over the AlGaN:Si layer; and in saidstep of forming the radiation-emitting active structure, said activestructure is formed on a surface of the GaN:Si layer.
 10. The method ofclaim 7, wherein the method comprises the steps of: forming the bufferlayer by a. forming an AlGaN:Si layer having a thickness of a fewhundred nanometers over the substrate, and b. forming a GaN:Si layerhaving a thickness of between 1 μm and 3 μm over the AlGaN:Si layer; andin said step of forming the radiation-emitting active structure, saidactive structure is formed on a surface of the GaN:Si layer.
 11. Thelight-emitting diode chip of claim 2, wherein the buffer layer comprisesa series of buffer layers including an AlGaN:Si layer and a GaN:Si layerlocated downstream thereof in a direction of growth, the GaN:Si layerhaving a thickness of between 1 μm and 3 μm and a surface that forms theepitaxial surface for epitaxy of the active structure.
 12. Thelight-emitting diode chip of claim 3, wherein the buffer layer comprisesa series of buffer layers including an AlGaN:Si layer and a GaN:Si layerlocated downstream thereof in a direction of growth, the GaN:Si layerhaving a thickness of between 1 m and 3 μm and a surface that forms theepitaxial surface for epitaxy of the active structure.
 13. Thelight-emitting diode chip of claim 2, wherein the active structure has asingle-quantum-well structure or a multiple-quantum-well structure thatcontains the In-rich zones.
 14. The method of claim 6, wherein thesubstrate comprises SiC.
 15. The light-emitting diode chip of claim 1,wherein the epitaxial surface of the buffer layer is un-etched.
 16. Thelight-emitting diode chip of claim 1, wherein the epitaxial surface ofthe buffer layer is free from grooves.
 17. The light-emitting diode chipof claim 1, wherein the epitaxial surface of the buffer layer isessentially flat.
 18. The light-emitting diode chip of claim 1, whereinthe epitaxial surface of the buffer layer is free from etchedstructures.
 19. The light-emitting diode chip of claim 1, wherein theepitaxial surface of the buffer layer is essentially free from grooves.20. The light-emitting diode chip of claim 1, wherein the light-emittingdiode is arranged in the following sequence of layers comprising: thesubstrate substantiality comprising SiC; an AlGaN:Si layer which is indirect contact with the substrate; a GaN:Si layer which is in directcontact with the AlGaN:Si layer; and the active structure which is indirect contact with the GaN:Si layer.